Wear leveling method and apparatus for nonvolatile memory

Abstract

A wear leveling apparatus uniformly distributes wear over a nonvolatile memory containing a plurality of memory blocks. The wear leveling apparatus includes a memory unit for storing a record of cold block candidates in the nonvolatile memory and a control unit configured to update the memory unit and release the cold block candidates under a threshold condition. The control unit selects a new memory block to replace one cold block candidate in the memory unit when the cold block candidate is matched with a written address in a write command for the nonvolatile memory. The cold block candidates remained in the memory unit are identified as cold blocks when the nonvolatile memory has been written more than a predetermined write count threshold. The memory blocks with infrequent erasure can be identified and released to uniformly distribute wear over the nonvolatile memory.

Description

BACKGROUND [0001] 1. Field of the Invention [0002] The present invention relates generally to a method and apparatus for extending the life of a memory device and, more particularly, to a wear leveling method and apparatus for nonvolatile memory. [0003] 2. Background of the Invention [0004] Nonvolatile memories such as flash memories do not require a power source to retain their memory content. Additionally, flash memories are generally compact size, and they have low power consumption because they do not contain moving parts. Accordingly, flash memories have been considered to be good replacements for conventional hard and floppy disk drives. As a result, flash memories are extensively used for consumer products, such as digital still cameras (DSCs), mobile phones and portable MP3 players. [0005] One major limitation for flash memories is the inability to directly program flash memory cells. In a typical use, each flash memory cell that is stored with data is erased before new data...

AI Technical Summary

Benefits of technology

[0008] The present invention provides a wear leveling method and apparatus for nonvolatile memory. In the preferred embodiment of the invention, the wear on the nonvolatile memory is leveled with high efficiency. Furthermore, the method provides the ability to change the accessing pattern of static area of the nonvolatile memory.

Problems solved by technology

One major limitation for flash memories is the inability to directly program flash memory cells.

Since flash memory is characterized in term of finite erase-write cycles, the flash memory has defective risk when some of its cells are erased beyond the finite cycles.

The problem is more serious in a flash memory that stores system programs because such flash memory has even fewer chances to update or modify.

However, the wear-leveling method disclosed in this patent does not account for static area in the flash memory.

Moreover, the provision of the re-map table for all flash memory cells is a considerable overhead cost for the flash memory.

However, this wear leveling method does not provide any criterion for selecting memory cell and unwanted erasure may be performed to the frequently erased units.

Images